X-ray diffractometer

ABSTRACT

An X-ray diffractometer has a yoke on which a crystal is mounted so that a particular rational axis thereof intersects the axis of the X-ray beam at a predetermined angle. A direct counting detector mounted on the yoke is selectively positionable in both azimuth and elevation with respect to the particular rational axis of the crystal. The yoke is constructed and arranged to effect precession of both the particular rational axis of the crystal and the detector about the axis of the beam.

ite States atent Rabinovich et al.

[45] Apr. 17, 1973 X-RAY DIFFRACTOMETER Inventors: Dov Rabinovich, Rehovoth, Israel; Gerhard M. J. Schmidt, deceased, late of Rehovoth, Israel by Ester Schmidt, administrator Yale Research and Development Co., Ltd., Rehovoth, Israel Filed: Jan. 5, 1972 Appl. No.: 215,486

Assignee:

Related U.S. Application Data Continuation-impart of Ser. No. 37,202, May 14,

I970, abandoned.

Foreign Application Priority Data May 20, 1969 Israel ..32247 US. Cl ..250/5L5, 250/52 Int. Cl. ..GOln 23/20 Field of Search ..250/5 l .5

[56] References Cited OTHER PUBLICATIONS Elimination of Spot Doubling In Precession Photography, J. N. Einstein Journal of Applied Crystalography 1970 pp. 180-181 (9/8/69).

Primary Examiner-James W. Lawrence Assistant ExaminerC. E. Church Attorney-Browdy and Neimark 5 7 ABSTRACT An X-ray diffractometer has a yoke on which a crystal is mounted so that a particular rational axis thereof intersects the axis of the X-ray beam at a predetermined angle. A direct counting detector mounted on the yoke is selectively positionable in both azimuth and elevation with respect to the particular rational axis of the crystal. The yoke is constructed and arranged to effect precession of both the particular rational axis of the crystal and the detector about the axis of the beam.

14 Claims, 6 Drawing Figures PATENTED APR] 7 I973 SHEET 1 BF 5 PATENTEDAPR 1 H915 3,728,541

SHEET 2 BF 5 Inventor;

.m/ 77, Jamar A Home yg PAIENIEBA 3.728.541

SHEET 3 0F 5 M giiwgu/w Attorney;

X-RAY DIFFRACTOMETER The invention relates to an improved X-ray diffractometer. The present application is a continuation-inpart of a co-pending application Ser. No. 37,202 filed May 14, 1970 now abandoned.

X-ray techniques have been widely used for many years in the study of the structure of matter and are capable of yielding detailed information on the structure of complicated molecules. The main disadvantage, however, in the use of such X-ray techniques is to be found in the extremely large amount of data which is required for structural analysis and which can amount, even in relatively modest cases, to well over 1000 individual spectra.

Two main techniques are employed in order to record the intensities of X-ray spectra. The first technique involves photographically recording the X- rays whilst the second technique involves counting the individual X-ray quanta by means of a radiation counter such as a geiger, proportional or scintillation counter.

Whilst the use of photographic techniques involve X- ray cameras which are relatively cheap, compact and simple in design and operation and have the advantage of yielding a permanent record, the integrated intensity of each reflection must be estimated either visually or photometrically from the density of the corresponding spots on the film and this procedure is slow and yields only relatively low quality data.

Radiation counters, on the other hand, are commonly used with diffractometers where each reflecting plane of the crystal is successively brought into its Bragg angle and the integrated intensity of the reflection from that plane is measured directly by the counter. The disadvantage associated with conventional apparatus using radiation counters lies in the complexity of the means by which the crystal is oriented in the beam and the detector brought into a known position both in relation to the crystal and the incident X-ray beam. Such means conventionally take the form of complex mountings for the crystal and the detector to give each the required degrees of freedom to properly orient the crystal and the counter. Depending on the type of cradle used, three or four angular settings are required in order to establish the desired orientation of the crystal relative to the beam and the required position of the detector relative to the crystal. As a consequence conventional apparatus is very expensive and requires relatively large and costly computers for control and operation.

It is an object of the present invention to provide a new and improved X-ray diffractometer using a direct counting device wherein the above referred to disadvantages are substantially reduced or overcome.

The present invention is based on the so-called coneaxis method described in full detail in the book The precession method by MJ. Buerger, published by .iohn Wiley and Sons, copyright 1964.

The following is a short summary of the method including the definition of parameters and concepts essential for the understanding of the mode of operation of the present invention.

The cone-axis method makes use of the fact that the diffracted reflections of the various planes of a crystal, irradiated by an X-ray beam, lie along the generators of the Laue cones co-axial with rational directions in that crystal. The term rational direction means here, a direc tion in the crystal defined by a vector Fn Z "217 n 0 where a, b and care vectors specifying the unit cell of the crystal under consideration and n n and n;, are small integers.

in order to obtain a cone-axis photograph the socalled Buerger precession camera may be used in which a photographic plate is fixed in a plane perpendicular to a particular rational direction of a crystal that is mounted in such a way as to permit that particular rational direction to precess about the in incident beam at a preselected angle u, without undergoing any pure rotation. The various orders of the Laue cones associated with the particular rational direction will intercept the photographic plate and define a set of concentric circles. Thus, during one full precession cycle, the various planes of the crystal are brought, each at its own specific phase of the cycle, into their reflecting positions and the reflected beams are recorded on the film as spots of different densities arranged in such a manner as to form the set of concentric circles described above. Each reflection is, conventionally, specified by three integers, hkl, known as the Miller indices of that reflection; the precession phase angle, mentioned above, of a given reflection hkl will therefore be denoted by I' Similarly, the azimuth angle of the spot associated with the hkl reflection, which is measured around the circle from a predetermined point, is denoted by All reflections lying on the nth circle (nth Laue cone) have one Miller index, n, in common and are said to belong to the nth order or level. All such nkl reflections have the same elevation angle 11, i.e., the halfopening angle of the nth Laue cone, and a circle radius r,,. In this manner each and every reflection is uniquely specified by the following parameters: the precession angle ;1., the elevation angle of the nth order 11,,, the phase angle l and the azimuth angle da Given the uni t cell dimensions and chosing the rational direction 1 and the precession angle u, the rest of the parameters may be calculated by appropriate crystallographic formulae.

In the X-ray diffractometer of the present invention, the photographic plate of the Buerger precession camera used to obtain cone-axis photographs is replaced by a radiation counter whose aperture is selectively positionable in elevation 11 and azimuth d). The photon-sensitive area of the counter is suitably masked so as to permit the recording of only one reflection at a time and to cut down the amount of background radiation. The angular opening Ad), and the radial height, Ar, chosen so as to exclude unwanted reflections and to minimize the background count, are computed from the known unit cell parameters, the instrument parameters, the radiation wave length and the physical dimensions and properties of the crystal.

-By choosing a particular rational direction and by fixing the mechanical parameters of the instrument, i.e., the precession angle 1, the aperture radial distance r,,, the angular opening and radial height of the aperture, Ad: and Ar,,, the nth order (nth circle of the set of concentric circles) is selected and all reflections of this order may now be measured successively. Thus, in order to record the intensity of a nkl reflection the particular rational direction is precessed to the required phase angle I' and, the aperture is rotated about the rational direction to the required azimuth angle 4%, At these angular positions one, and only one, reflection will be recorded; the output of the detector yields the integrated intensity of this reflection. By changing the pair of angles I and d), the complete set of the nth order reflections can be measured.

BRIEF DESCRIPTION OF THE INVENTION Briefly, a direct radiation detector is coupled to a crystal so that both the detector and a particular rational axis of the crystal precess together about an incident X-ray beam. The detector, which is mounted so as to be selectively positionable in both azimuth and elevation with respect to the particular rational axis of the crystal, is suitably masked to limit its field of view in such a way as to exclude unwanted reflections, and reduce background radiation.

In one embodiment of the invention the detector is mounted on an axial end of a drum which is rotatable about the particular'rational direction of the crystal. The detector is eccentrically positioned on the drum so that the axis of the detector is parallel to the drum axis. Rotation of the drum will place the detector at the required azimuth angle. The elevation angle is established by suitable adjustment to the aperture means that mask the detector, such adjustment serving to effectively move the aperture radially of the surface.

Alternatively, or in addition, the detector can be radially displaceable on the drum.

In another embodiment of the invention, the drum is in the form of a ring to which is attached a cylindrical guide, the axis of which is normal to the rotational axis of the ring and passes through the point where the X- ray beam intersects the axis of the ring. The detector, in this embodiment, is slidably mounted in the guide for arcuate movement about the crystal to establish the desired elevation angle of the detector. The azimuth angle is established by suitably rotating the ring. In this embodiment, the detector axis is always aligned with v the reflected beams. In the first described embodiment,

the detector axis is inclined with respect to the reflected beams.

BRIEF DESCRIPTION OF DRAWINGS For a better understanding of the present invention, and to show how it can be carried out in practice, reference should be made to the accompanying drawings, wherein:

FIG. 1 is a schematic representation showing the mounting of a crystal in a Buerger precession camera in preparation for making a cone-axis photograph;

FIG. 2 is a top plan view of the first embodiment ofa diffractometer according to the present invention;

FIG. 3 is a front elevation of the diffractometer shown in FIG. 1;

FIG. 4 is a side elevation of the diffractometer shown in FIG. 1 with the gimbal rotated to make an angle ,u. with the incident X-ray beam; and

FIG. 5 is a schematic representation of a precession diffractometer system in accordance with the present invention; and

FIG. 6 is a pictorial perspective showing a second embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION In the first embodiment of the invention shown in FIGS. 2 5 of the drawings, a first vertical gimbal fork 5 comprises a pair of vertically disposed spaced gimbal limbs 6 and 7 coupled together by a horizontal gimbal beam 8. A vertical tube attached to beam 8 is rotatably mounted on a vertical gimbal shaft 9 which is, in turn, fixedly mounted on a turntable 10. Fork 5 is thus vertically rotatable about axis 101 of shaft 9. The turntable 10 is rotatably mounted on base beams 11 which are supported with respect to a support surface by means of levelling screws 12. The turntable 10 is provided with a turntable lock 13 by means of which the turntable can be locked in any desired angular position with respect to the base beams 1 l.

A pair of short horizontally aligned gimbal shafts 14 and 15 are respectively rotatably mounted in ball bearings 16 and 17, journalled in the upper bifurcated ends of the vertical gimbal limbs 6 and 7. The horizontal gimbal shaft 14 is formed integrally, on one end thereof, with an extended horizontal shaft 18 of the gimbal which is, in turn, coupled to a goniometer head 19 which supports a crystal 20. The crystal is located at that point at which the axis 101 intersects the axis 102, which is the common axis of aligned horizontal shafts 14 and 15. The other end of the horizontal gimbal shaft 14 is coupled to a crystal translation adjustment mechanism 21 via a dial 23 and dial axis vernier 22. The mechanism 21 is provided with a crystal translation adjustment screw 24 for selectively moving the crystal along the axis 102.

A second gimbal fork 25 comprises a pair of yoke arms 26, 27 which project into the bifurcated ends of the vertical gimbal fork limbs 6, 7 and are rigidly secured to the short horizontal gimbal shafts 15, 14. The yoke arms 26, 27 are rigidly secured together by rear andintermediate cross beams 28 and 29. The second gimbal fork 25 is thus mounted on the first gimbal fork 5 for pivotal movement about the horizontal axis 102.

A support shaft 103, whose axis passes through theintersection of the axes 101 and 102, projects through and is rotatably mounted in the rear cross beam 28. Vernier 31, rigidly mounted on beam 28, cooperates with 11 dial 30 rigidly attached to and rotatable with shaft 103. The free end of shaft 103 projects into and is rotatably mounted in a suitable bearing in coupling collar 32 which can freely slide on arcuate member 33 and thus position fork 25 relative to limbs 6 and 7 of fork 5 so that the axis 104 of shaft 103 will make the desired angle p. with a horizontal X-ray beam passing through the intersection of axes 101 and 102. In such position, the collar 32 can be clamped to arcuate member 33 which itself is rigidly attached to a I drive shaft 34 journalled in a frame 35 within which is supported a I drive motor 36. The output of the motor 36 is transmitted via a worm and gear 37 coupled to the drive shaft 34. By means of locking screw 40, the I dial 38 is rigidly attached to and rotatable with shaft 34. Dial38 is cooperable with vernier 39 which is rigidly attached to frame 35.

The end of shaft 103 remote from the bearing in collar 32 is attached to and supports one end of radiation counter drum 41 which is mounted in fork 25 for rotation about the axis 104 of shaft 103. The other end of the drum 41 is mounted in an annular drum frame 42 by means of angularly spaced apart drum supports 43, respectively held in support holders 44 secured to the frame 42 and respectively provided with drum support adjustment screws 45. The rear end of the drum is formed integrally with a qb gear wheel 46 which meshes with a 4: pinion 47 coupled to an output shaft 48 of a 4 drive motor 49 also supported by the yoke 25. Thus the drum 41 can be rotated about axis 104 through the angle 4) by the drive motor 49 whilst supported on the drum supports 43.

Located within the drum 41 is a radiation counter 50 (shown in dotted lines in FIG. 3) whose longitudinal axis is parallel to, but spaced apart from the longitudinal axis 104 of the drum 41. The front aperture of the counter 50 is located opposite a sector-like aperture 51 formed in an end face of the drum. Selective rotation of drive motor 49 will rotate the counter about axis 104 until the photon-sensitive surface is positioned at the desired azimuth angle relative to axis 104.

Superimposed on the end face of the drum is a first metal disc which is supported on the end face for rotation about axis 104. A sector-like aperture 52 formed in the first metal disc corresponds to the sector-like aperture formed in the fixed end face. Thus, by rotating the first metal disc with respect to the end face of the drum, the apertures 51 and 52 may be misaligned to the extent necessary to mask of the photon-sensitive surface of the counter 50 except for the aperture 53 having the desired angular width Ad The relative position of the two apertures 51 and 52 and in consequence the magnitude of A4) can be measured by means of a rotatable disc dial and vernier arrangement 54. A second metal disc 55 is also rotatably mounted on the end face of the drum and is provided with a plurality of annular slots 56 of differing radii corresponding to the differing radii of the cone axis circles. The radial width of each slot establishes the height Ar of the aperture for the counter. By rotating the second disc on the end face of the drum, a selected one ofthe slots 56 can be positioned opposite the aperture 51 and 52 to establish the radial position r of the aperture. A pair of radially spaced apart locking screws 57 and 58 are provided for securing the additional disc 55 in the required position.

The end face of the drum, in cooperation with the first and second discs, selectively masks the photonsensitive surface of the counter establishing a detector with a limited field of view. By rotating the drum on the yoke 25, and by rotating the first-and second discs on the end face of the drum, the detector can be positioned at azimuth and elevation angles with respect to the rational direction I of the crystal corresponding to a particular reflection to be studied. In addition, the required aperture size Ad) and Ar to prevent recariation of simultaneous reflections will also be achieved.

Finally, an X-ray collimator 59 is supported in a collimator holder 60 and is provided with a collimator lock mechanism 61, the collimator holder 60 being located fixedly with respect to the turn table 10. The collimator 59 is aligned with the I drive shaft 34.

In operation the precession diffractometer turntable is rotated so as to align the collimator 59 in the direction of the X-ray source and the turntable 10 is clamped in this position by means of the turntable lock 13. The horizontal axis dial mechanism 21 is then rotated so as to bring the horizontal axis 102 into the appropriate position wherein the desired rational direction of the crystal is correctly orientated with respect to the collimated X-ray beam. The collar 32 is thereupon unclamped and is slid on the arc member 33 until the axis 104 orients the crystal at the predetermined angle p. with respect to the incident X-ray beam. When so orientated the collar 32 is clamped in position.

The first metal disc on the end face of drum 41 is rotated so as to define a predetermined angular width of aperture A4: which, as indicated above, is predetermined in accordance with the conditions for avoiding the detection of unwanted reflections. Similarly, the second metal disc 55 is rotated so as to superimpose on the aperture that annular slot corresponding to the predetermined height Ar and radial position of the aperture in which measurements are to be effected. A detector is now established at the desired elevation angle to measure the reflected energy from a particular nth level of the crystal.

Measurement can now be obtained in any one of the following modes:

In accordance with a first mode of operation the and (1) drive motors 36 and 49 are actuated so as to set the instrument in the required P and da setting for any particular nkl reflection, the I' and d) settings being read on the respective dials 40 and 30. The instrument, (i.e., the crystal and the counter) is maintained stationary in this particular setting and the reflection intensity is measured over a predetermined period of time in terms of the electric pulses from the counter which are fed to a spectrometer which together with the counter constitutes a standard counting channel.

In accordance with a second mode of operation the drive motor 36 is arranged to displace the instrument to a value of I which corresponds to, but is somewhat less 7 than the predetermined value of I' corresponding to the particular reflection to be measured. The (1) drive motor 49 then rotates the drum to the required (b position and now, a predetermined number of discrete stepping pulses are successively fed to the I drive motorso as to drive the instrument by small discrete steps into and slightly beyond the predetermined P value, at each step the intensity of reflection being measured. In this way scanning of the range is obtained.

Preferably stepping motors are used for both the I and ti drives. These motors were chosen because they offer two important advantages over continuous motors. First, they can be conveniently used in open loop control logic, i.e., there is no need for feedback, from digitizer or other position detecting devices, to stop the motor when the required setting is achieved; a predetermined number of electrical pulses being all that is needed to rotate the motor to its specified settings. Secondly, such a motor may be electrically locked by applying direct current, thus avoiding drift of the drive shaft.

The motor drive preferably consists of an electronic pulse generator whose pulses are fed into the motors. Manual control switches can be provided for selecting the required motor operation and its sense.

An automatic control may be used to supervise the operationof the various components of the precession diffractometer system in order to collect the data of a complete level. As seen in FIG. 5, automatic control is effected by means of an on-line desk-top computer assembly 71. The computer assembly 71 consists of a desk-top calculator, a programmer and an auxiliary storage memory. An interface 72 connects the output of the computer assembly 71 to a motor drive control '73, to the spectrometer 74 and to a sealer printout control 75 and teletype unit 76. A suitable program controls the system. Input parameters for this program comprises (a) crystallographic parameters, (b) operation instructions, (c) status parameters. Using these data the computer assembly is capable of computing and controlling the data collection of a set of reflections belonging to a given level.

In the embodiment of the invention shown in FIGS. 2 of the drawings, the axis of detector 50 is substantially parallel to the axis 104 of the drum 41 and the support shaft 103, which axis is also congruent with the particular rational axis of the crystal. When stepping motor 49 is operated, detector 50 is caused to rotate about axis 104. The photon-sensitive surface of detector 50 under these conditions will not be normal to beams reflected from the crystal; and beams reflected from the crystal will impinge on the photon-sensitive surface of detector 50 at the elevation angle v,,.

Referring now to FIG. 6, the second embodiment of the invention is designated generally by reference numeral 200. The device of embodiment 200 includes a first gimbal fork 5, a second gimbal fork 25', support shaft 103, coupling collar 32, arcuate drive member 33, and I drive shaft 34. The first gimbal fork, the support shaft, the coupling collar, the arcuate drive member, and the I drive shaft in embodiment 200 are the same as the corresponding elements in the first described embodiment.

The second gimbal fork 25' comprises a first support ring 201, a second support ring'202 and a curved guide 203. Rigidly attached to and perpendicular to the plane of first support ring 201 are a pair of diametrically opposed bearing lugs 204 which form bearings for gimbal shafts l4 and 15. The axis 102 of these gimbal shafts is perpendicular to and intersects the axis 101 about which fork 5 is rotatable. The point of intersection is designated P. While not shown in FIG. 6, a shaft integral with gimbal shaft 14 extends toward the intersection of the axes 101 and 102 and carries a goniometer head which suitably supports, at point P, a crystal which is to be studied. This shaft is the same as shaft 18 of the first described embodiment.

The second support ring 202 is rotatably mounted on the first support ring 201. Axis 104, about which the second support ring 202 rotates, is congruent with the axis of support shaft 103. To provide for the angular positioning of ring 202 on ring 201, the outer circumference of ring 202 may be provided with gear teeth which mesh with a pinion 47 rigidly attached to shaft 48 of the aximuth motor 49. This motor is rigidly attached to support ring 201. By energizing motor 49, it is possible to rotate ring 202 about axis 104 and place the ring in any angular position.

Curved guide 203 is defined by a pair of arcuate ribs which diametrically span ring 202 and are rigidly connected thereto. The plane of each of these arcuate ribs is normal to the plane of ring 202. The inner curved surface of these ribs establish a cylindrical guide sur face, the axis of which surface is perpendicular to axis 104 and passes through the point P at the intersection of axes 101 and 102.

Slidably mounted on the ribs of curved guide 203 is adjustable clamp 205 which releasably carries detector 50. With this arrangement the axis of detector 50' will always pass through the point P at the intersection of axis 101 with axis 102 regardless of the location of the adjustable clamp 205 on the guide 203, and regardless of the angular position of ring 202 on support ring 201.

A U-shaped support 206 is attached to guide 203 in the middle thereof and extends away from the guide in a radial direction. The space between the legs of this support provide clearance for passage of detector 50' and adjustable clamp 205. Carried on the bridge between the two legs of support 206 is support shaft 103 whose axis is colinear with axis 104. The free end of shaft 103 projects into and is rotatably mounted in a suitable bearing in coupling collar 32 which can freely slide on arcuate member 33 and thus pivot for 25' about axis 102. In this manner axis 104 can be positioned at the desired angle p. with respect to a horizontal X-ray beam passing through the point P at the intersection of axes 101 and 102 by clamping the collar 32 to arcuate member 33 which itself is rigidly attached to I drive shaft 34 journalled in the same manner as in the previously described embodiment. Suitable scales and indicia may be provided in the embodiment shown in FIG. 6 to provide for reading out the angles v d) and 1 between the various components as shown in FIG. 6.

The operation of embodiment 200 is substantially the same as the operation of the first described embodiment except as to the manner in which the elevation angle of the detector is changed. Thus, collar 32 may be moved on arcuate member 33 until the plane of rings 201 and-202 is tilted to establish the axis 104 at the desired angle p. with the X-ray beam. In this position, axis 104 is colinear with a particular rational axis of a crystal under study. Knowing the angle 1 the detector 50' is moved on the ribs of curved guide 203 until the axis of detector 50 makes the angle 11,, with the axis of the X-ray beam. The detector is held at this location by tightening adjustable clamp 205. As shaft 34 is rotated by the I drive motor (not shown in FIG. 6), fork 5 will oscillate about axis 101 through an angle of 2 y. while, at the same time, gimbal fork 25' will oscillate about axis 102 through the same angle. With this arrangement, the particular rational axis of the crystal under study precess about the X-ray beam in a conventional manner. Motor 49 may be energized in a selective manner to position ring 202 so that the detector 50' is at the proper azimuth angle for the reflection under consideration. All three modes of operation described in connection with the first embodiment of the invention can be utilized with the embodiment shown in FIG. 6. Different Laue cones are investigated by changing the elevation angle v The detector 50' may be fitted with a suitable adjustable aperture for discriminating against simultaneous reflections.

What is claimed is:

1. An X ray diffractometer for positioning a crystal in an X-ray beam and measuring the intensity of reflected radiation comprising: a yoke on which a crystal can be mounted so that a particular rational direction thereof intersects the axis of the beam at a predetermined angle, a photon-sensitive detector movably mounted on the yoke and selectively positionable in azimuth and elevation with respect to the particular rational direction of the crystal, the output of the detector being proportional to the intensity of the reflected radiation intercepted by the detector, and the yoke being constructed and arranged to effect precession of both the particular rational direction of the crystal and the detector about the axis of the X-ray beam.

2. An X-ray diffractometer according to claim 1, wherein the yoke comprises a first gimbal fork mounted for pivotal movement about a first axis intersecting the beam at a right angle, a second gimbal fork mounted on the first fork for pivotal movement about a second axis perpendicular to the first axis and passing through the point where the beam intersects the first axis, a drive member mounted for rotation about the axis of the beam, and a pivotal connection between the drive member and the second fork, the axis of the pivotal connection passing through the point at which the first and second axes intersect with the beam.

3. An X-ray diffractometer according to claim 2, wherein the drive member is arcuate in shape, the center of curvature of the drive member being the point at which the first and second axes intersect the beam.

4. An X-ray diffractometer according to claim 3, including a drive motor for moving the drive member to preselected angular positions, and an azimuth motor for rotating the detector about the axis of the pivotal connection between the drive member and the second fork.

5. An X-ray diffractometer according to claim 4, including a drum rotatable on the second gimbal yoke about the same axis as the pivotal connection; the detector being mounted eccentrically in the drum and the azimuth motor serving to move the drum to preselected angular positions.

6. An X-ray diffractometer according to claim 5, wherein the drive motor and the azimuth motor are stepping motors that impart incremental movement to the drive member and the drum respectively.

7. An X-ray diffractometer according to claim 6, including motor control means for controlling the drive and drum motors in accordance with a computer controlled program.

8. A method for using the X-ray diffractometer according to claim 1, wherein the yoke is operated to cause precession of both the particular rational axis of the crystal and the detector about the beam direction, and the azimuth and elevation of the detector are periodically changed in a manner to cause the detector to map the intensity of the reflected beam.

9. An X-ray diffractometer according to claim 1, wherein the detector is constituted by a counter having an aperture defining means masking the counter and limiting the field of view of the detector for preventing unwanted reflections from reaching the surface.

10. An X-ray diffractometer according to claim 9, including a drum mounted on the yoke so as to be rotatable about the particular rational direction of the crystal, the counter being eccentrically mounted on the drum so that rotation of he drum changes the aximuth of the detector.

11. An X-ray diffractometer according to claim 1, wherein the axis of the detector is substantially parallel to the particular rational direction of the crystal.

12. An X-ray diffractometer according to claim 1 wherein the axis of the detector passes through the point where the beam intersects the particular rational direction of the crystal.

13. An X-ray diffractometer according to claim 4, wherein the axis of the detector passes through the point at which the first and second axes intersect with the X-ray beam.

14. An X-ray diffractometer according to claim 13 wherein the second gimbal fork includes a first support ring pivotally connected to the first gimbal fork, a second support ring mounted on a first support ring for rotation thereon about the axis of the pivotal connection between the drive member and the second gimbal fork, a curved guide diametrically spanning and rigidly connected to the second support ring for establishing a cylindrical guide surface whose axis of perpendicular to the axis of the pivotal connection between the drive member and the second gimbal fork and passes through the intersection of the first and second axes, the detector being adjustably mounted on the second support ring so that the axis of the detector is perpendicular to the cylindrical guide surface period.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTKGN vPatent No. 3,728,541 7 D d April 17, 1973 Inventofls) DOV RABINOVICH et a1.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

The Assignee should read:

--YEDA Research and'Development Co. Ltd."

instead of "Yale Research and Development Co. Ltd."

Signed and sealed this 26th day of March 1974.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents =ORM P0-1050 10-69 USCOMM-DC 60376-P69 U. 5. GOVERNMENT PRINTING OFFICE 2 i969 0-356-33l 

1. An X-ray diffractometer for positioning a crystal in an X-ray beam and measuring the intensity of reflected radiation comprising: a yoke on which a crystal can be mounted so that a particular rational direction thereof intersects the axis of the beam at a predetermined angle, a photon-sensitive detector movably mounted on the yoke and selectively positionable in azimuth and elevation with respect to the particular rational direction of the crystal, the output of the detector being proportional to the intensity of the reflected radiation intercepted by the detector, and the yoke being constructed and arranged to effect precession of both the particular rational direction of the crystal and the detector about the axis of the X-ray beam.
 2. An X-ray diffractometer according to claim 1, wherein the yoke comprises a first gimbal fork mounted for pivotal movement about a first axis intersecting the beam at a right angle, a second gimbal fork mounted on the first fork for pivotal movement about a second axis perpendicular to the first axis and passing through the point where the beam intersects the first axis, a drive member mounted for rotation about the axis of the beam, and a pivotal connection between the drive member and the second fork, the axis of the pivotal connection passing through the point at which the first and second axes intersect with the beam.
 3. An X-ray diffractometer according to claim 2, wherein the drive member is arcuate in shape, the center of curvature of the drive member being the point at which the first and second axes intersect the beam.
 4. An X-ray diffractometer according to claim 3, including a drive motor for moving the drive member to preselected angular positions, and an azimuth motor for rotating the detector about the axis of the pivotal connection between the drive member and the second fork.
 5. An X-ray diffractometer according to claim 4, including a drum rotatable on the second gimbal yoke about the same axis as the pivotal connection; the detector being mounted eccentrically in the drum and the azimuth motor serving to move the drum to preselected angular positions.
 6. An X-ray diffractometer according to claim 5, wherein the drive motor and the azimuth motor are stepping motors that impart incremental movement to the drive member and the drum respectively.
 7. An X-ray diffractometer according to claim 6, including motor control means for controlling the drive and drum motors in accordance with a computer controlled program.
 8. A method for using the X-ray diffractometer according to claim 1, wherein the yoke is operated to cause precession of both the particular rational axis of the crystal and the detector about the beam direction, and the azimuth and elevation of the detector are periodically changed in a manner to cause the detector to map the intensity of the reflected beam.
 9. An X-ray diffractometer according to claim 1, wherein the detector is constituted by a counter having an aperture defining means masking the counter and limiting the field of view of the detector for preventing unwanted reflections from reaching the surface.
 10. An X-ray diffractometer according to claim 9, including a drum mounted on the yoke so as to be rotatable about the particular rational direction of the crystal, the counter being eccentrically mOunted on the drum so that rotation of the drum changes the aximuth of the detector.
 11. An X-ray diffractometer according to claim 1, wherein the axis of the detector is substantially parallel to the particular rational direction of the crystal.
 12. An X-ray diffractometer according to claim 1 wherein the axis of the detector passes through the point where the beam intersects the particular rational direction of the crystal.
 13. An X-ray diffractometer according to claim 4, wherein the axis of the detector passes through the point at which the first and second axes intersect with the X-ray beam.
 14. An X-ray diffractometer according to claim 13 wherein the second gimbal fork includes a first support ring pivotally connected to the first gimbal fork, a second support ring mounted on a first support ring for rotation thereon about the axis of the pivotal connection between the drive member and the second gimbal fork, a curved guide diametrically spanning and rigidly connected to the second support ring for establishing a cylindrical guide surface whose axis of perpendicular to the axis of the pivotal connection between the drive member and the second gimbal fork and passes through the intersection of the first and second axes, the detector being adjustably mounted on the second support ring so that the axis of the detector is perpendicular to the cylindrical guide surface period. 